It represents a constant that is multiplied by the error. The Proportional constant represents the area in which the controller is actually controlling the process and determines the band of operation. The Proportional, Integral, and Derivative constants are used to calculate what the output should be relative to the measured error. The response characteristics of the controller are determined by the PID constants provided to the controller. If control is not aggressive enough (over-damped), the system may require too much time to recover-or not recover at all. If the controller is too aggressive (under-damped), it may cause the process to become unstable and oscillate. Each time an error is calculated, the controller must decide how much to alter the process. If an error exists, the controller adjusts its output to alter the process to bring it closer to the desired point, thus minimizing the error. The PID controller measures the output of the process and calculates the difference (error) between what is measured and the set point. While these controllers can be built using analog circuits, implementing them using a digital controller provides greater flexibility in adjusting the control algorithm and in fine-tuning the controller settings. The purpose of a controller is to compensate for the effects of disturbances on process variables and to force a process variable to track a desired set point. Industrial controllers utilizing this technique are used for controlling processes like those found in chemical plants, those for temperature control, for certain automotive applications, etc. One of the most common automatic control methods is the Proportional-plus-Integral-and-Derivative (PID) controller. *Adapted from PID Control with ADwin, by Doug Rathburn, Keithley Instrumentsīy Terry Nagy, Computer Aided Solutions, LLC. Processors with Sub-Microsecond Response Times Control a Variety of I/O
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